It has already been happening for several years now, it's just accelerated since Trump. Even before his first term there was a "negative brain drain" of educated workers no longer coming into the US because the benefits (paid time off, health care, etc) are so much worse compared to other countries, even when considering the higher pay. America used to rely on a steady stream of incoming highly educated workers.

But now there is a huge amount of well established academics leaving for Canada, EU, or anywhere else that will pay them. I work in a physics department at a large R1 university in a very liberal state, and we are losing 4 (that I know of) high regarded professors just this year alone moving to other countries.

The brain drain is here, and won't be reversing course even if Trump suddenly disappears. We would have to completely change how we reward work and our failing healthcare system for anything to change.